Reflex Terahertz Spectrum Imaging Technology

Since1980s, with the rapid developments of ultrafast laser technology, thegeneration of terahertz (THz) radiation using photoconductive antenna (PCA) andoptical rectification (OC), and the detection of THz radiation using electro-opticsampling (EOS) and photoconductive antenna were becoming mature. THztime-domain spectroscopy (THz-TDS) and imaging technologies have been progressedsignificantly. With the advantages of low energy and easily penetrate many dielectricmaterials, THz-TDS and imaging have huge potential applications in nondestructiveinspection, security examination and identification, and so on.In this thesis, a reflection THz-TDS system was designed and set up based on thePCA generation and EOS detection. In order to improve the detection efficiency, thesystem was optimized by adjusting the angles of the electro-optic crystal. To overcomethe shortcoming of the low sampling speed, fast optical delay line was employed andthe time constant of lock-in amplifier was carefully optimized.Researches on THz imaging were carried out using home-made THz system. Theprocess of THz imaging was optimized by the reasonable program design and the fastoptical delay line. The time consumed in the THz imaging process was greatlyshortened. The reflection THz images of covered shaver and IC card were obtained.Different methods were used to get the THz images of these samples and the internalconfiguration of the IC card was analyzed.The THz-TDS signals and THz images were processed by the data and imageprocessing technologies. To improve the signal to noise ratio (SNR) of the THz-TDSsignal, wavelet de-noising technique was used. Image processing techniques wereemployed to enhance the contrast and get the better profiles of THz images, and thequality of the THz image was improved.